The performance of an oven is determined by how effectively various heat transfer mechanisms can be delivered for heat treating a work-piece (food item) to produce a unique commercial advantage. In general, different food substrates require very specific processing treatments to deliver the sensory attributes desired by consumers. Food processors strive to deliver these specific food attributes through continuous and repeatable large-scale industrial cooking systems. Such cooking systems may utilize one or more heat treatment steps involving different heat transfer mechanisms to affect the final food item outcome in terms of product quality, flavoring, color development, food safety and/or economic considerations.
Simply applying heat does not necessarily produce the desired food attributes and it is important to understand what brings about various desired attributes. For example, heat processing conditions, sequences and equipment needed for poultry, beef, pork, and bakery items can vary significantly. Flexibility of heat treatments, the timely application of appropriate heat transfer mechanisms and overall equipment and system design are crucial to bringing about the qualities that are inherent and unique to the particular food substrates. Furthermore, food item appeal and texture associated with coatings external to the food substrate are also enhanced through precise control and conditioning of heat delivery.
Current commercial oven systems may utilize a steam chamber to pre-heat a food substrate prior to cooking or baking in an oven chamber. Such steam chambers typically operate at about 190° F. (about 88° C.) at the inlet to about 250° F. (about 120° C.) at the discharge end of the chamber. This is due to cold air and hot air infiltration effects occurring at the inlet and discharge respectively. As a result, the conditions in the steam chamber never reach saturation or even close to it. Therefore, at partially saturated conditions this chamber, which relies on condensation of water vapor onto the surface of the food substrate or work-piece to affect a rise in core temperature of the work-piece, is rather limited in available energy for transfer. Furthermore, such systems have performance limitations and process variations due to conditions prevailing upstream of the oven and/or outside room environment. Left uncontrolled these conditions can have a significant impact on cooking performance. These variations will have adverse effects on the heat transfer performance at initial and the most crucial stage of a cooking process thereby producing inconsistent product output which may lead to increased standard deviation of product temperatures across the belt width of a continuous system.
When fully saturated steam is introduced to a conventional steam chamber positioned at the inlet of an open continuous oven, the steam (i.e., the saturation level) is affected by air and/or vapor infiltrating from outside of the oven as well as process air migrating from the oven into the steam chamber. The amount air and/or vapor that migrates from the oven into the steam chamber is dependent upon the pressure differential at the interface between the oven and the steam chamber. Circulation fans in the oven typically produce a positive pressure differential between the oven and the steam chamber which may cause a hot air/vapor mixture to migrate from the oven into the steam chamber. The influx of the air/vapor mixture into the steam chamber thereby causes the steam to assume a partially saturated condition. The induced pressure differential is influenced by the relative operating conditions (i.e., temperature, fan speed and humidity) between the oven and the steam chamber. A small change in the steam saturation level within the steam chamber may result in relatively large changes in temperature across the belt width within the steam chamber and can result in non-uniform heating of the food item.
Air/vapor infiltration into the steam chamber increases the amount of air within the steam chamber to produce a partially saturated condition. This causes the effective heat transfer delivery rate to the product to be reduced and therefore increases the time needed to achieve a desired core temperature (dwell time). Increased dwell time of a food item within the steam chamber and through the entire cooking process will result in reduced product yields and throughput and increase operating costs. Additionally, air/vapor infiltration may cause inconsistent and/or variable condensation heating which will be detrimental to achieving desired product quality attributes and may pose food safety concerns.
Commercial food producers generally adjust for non-uniform heating by over-cooking food items. Typically, food items will be cooked longer at higher humidity or higher temperatures to ensure that minimum cooking temperatures are achieved within the largest food item on nay given batch on a continuous basis to insure food safety. However, cooking at higher temperatures than necessary combined with longer heating times may produce poor product quality and reduce throughput and yield.